1. Field of the Invention
The present invention relates to a method of and a device for cooling a brake fluid.
2. Prior Art
There is known a conventional brake operating unit comprising a brake element that is a drum brake or a disc brake. That is, a fluid (liquid) pressure generating unit composed of, e.g., a master cylinder is actuated by depressing a brake pedal to supply a brake fluid to a cylinder of the brake element, the amount of the brake fluid corresponding to the depressed amount of the brake pedal, so as to generate a braking force, or the fluid pressure generating unit is released by releasing the brake pedal from being depressed to discharge the brake fluid in the cylinder of the brake element so as to release the braking force. At the time of releasing the brakes, the brake fluid in the cylinder of the brake element is discharged therefrom by the elastic restoring force of a shoe return spring in case of a drum brake, and by that of a seal ring in case of a disc brake. The brake element generates a braking force when friction materials of brake shoes or pads slidably contacts a brake drum or disc while generating a frictional heat.
In such a conventional brake operating unit, however, only a single brake line (fluid channel) is connected to the cylinder of brake element for both supply and discharge of the brake fluid, so that the brake fluid only moves into or out of the cylinder therethrough but it is not substantially exchanged with a brake fluid of low temperature. As a result, frequent repetition of applying the brakes generates a vapor-lock to cause a dangerous state of brake failure. The vapor-lock is a phenomenon caused by the failure of normal transmission of pressure when the brake fluid in the cylinder of a brake element is overheated so that a part of it is vaporized and gasified. Although it is proposed to cool the brake element by sending air thereto for preventing the vapor-lock, a brake element which can prevent the vapor-lock with certainty has not appeared yet.